Garden Myth: Gravel in Pots and Containers

By: Julie Day

Flower pots don’t need gravel in the bottom.

I’ve always been told to put a layer of gravel in the bottom of a flower pot before planting. Is this really necessary?

Actually, it’s a myth, but it’s one that even I believed for many years. The common belief is that a layer of gravel in the bottom of pots will improve drainage and keep the soil from spilling out, and besides, that’s how we’ve always done it, so it must be right.

Here are the facts about using gravel in potted plants.

Why Gravel Doesn’t Improve Drainage

The gravel myth is based on a mistaken idea that it will increase drainage. Follow my logic here and see if we can debunk this idea:

Gravel vs. Soil: Gravel does drain water – obviously, water runs through gravel faster than soil. However, the opposite is also true: soil holds water better than gravel.

Soil is like a sponge.

Soil Acts Like a Sponge: Water won’t run out into the gravel, or out of the pot, or anywhere, until the soil is saturated. If you don’t believe me, try laying a sponge on top of a pile of gravel, then pour water into the sponge. Does the gravel make the sponge drain faster? No, the sponge fills up, and it won’t drip until it can’t hold another drop.

Not Enough Soil: Just like with a sponge, water naturally settles toward the bottom of the soil. But because you’ve partially filled your pot with gravel, that soggy soil bottom is now higher (and closer to your plant’s roots). Basically it’s like having a smaller pot!

Poor Results: So, you end up with an unhappy, crowded plant sitting in too wet soil, and you’ve wasted valuable pot space with gravel that’s doing no good.

Drainage Made Easy:

Your plants will be happier if you uniformly increase the drainage of the soil itself. Choose high-quality potting soil that is well draining. And if your plants need even more drainage, instead of putting gravel in the bottom of your pot, try mixing in perlite, PermaTill, or organic matter into your potting soil to increase drainage throughout the pot.

Gardening Tip

If you’re worried about soil washing out of the bottom of your pot, put a paper coffee filter, a piece of screen, or a shard of pottery over the holes before adding dirt. Usually, though, drainage holes are small enough that this isn’t a problem.

How to Use Gravel with Potted Plants

If you want to put gravel to work with your potted plants, use it outside the pot. Put a layer of gravel in your plant’s drainage tray, or down inside a decorative planter, then sit your plant pot on top. The gravel will hold water and increase humidity, while keeping your plant’s roots up out of the puddle.

Gravel comes in handy when sitting a plant inside a decorative planter.

Gravel in Non-Draining Pots

The best type of flower pot has drainage holes in the bottom, and you should always shop for pots that drain. But for pots that don’t have holes, some people put gravel in the bottom of the pot, to create a sort of internal “drainage tray” to collect water under the dirt. Some people are able to get this to work, but it can cause problems, including:

Overwatering: You can’t see the gravel, so how do you know how much water is down there? If water builds up, the soil will turn into a soggy mess, and your plant will be on the fast track to root rot.

Poor Growth: Water, nutrients, and air move through soil using capillary action, sort of like a straw. If you plug the bottom of a straw, it stops working, and when you plug up the bottom of your plant’s soil (by trapping it in a non-draining pot), it stops working, too.

Disease: If you’ve ever opened a container that’s been in your refrigerator too long, you’ve learned firsthand what happens when moisture and organic material are trapped in a space with no air flow. A moldy mess!

40 Comments on “Garden Myth: Gravel in Pots and Containers”

What potted plants don’t have roots that grow to the bottom of the pot? Adding a layer of gravel helps those bottom roots from sitting in standing water and helps provide oxygen. Your myth assumes your plants root system doesnt reach the bottom or ever out grows it pot and eventually root locks or if saturated root rots.

I just changed my furnace filter, and thought, what a great way to reuse it to keep soil from washing out of my large, potted plants! Only dust (which is microscopic dirt) has been collected in it! Very porous, and a good way to reuse, and it’s 16x 20, so it can be used for at least one, and several other small pots, depending on size. Any thoughts.? Worth a try.

Why change something that has work for my plants for many years They are healthy ,happy and thriving in pots with holes and gravel 1″size. Never have rot root or pest from unsterile rocks out of yard. I just wash them dry in sun and use them. I do use good potting soil and that’s it. Fertilize plants a few times a year. Everyone thinks I have a green thumb. If it not broken ,why change what works for you!

I have 5 terrariums. All 5 are in glass containers with gravel on the bottom. I’ve never actually seen water go into the bottom where the gravel is…maybe a few drops. My plants have been in their containers for exactly 1 year. I’ve dug them out and repotted to add additional plants, etc. None of them have ever had root issues. You just have to learn how to water carefully. Literally shove your finger into the dirt to see if it’s still damp. Another method is to shove a rock into the dirt and check to see if it’s still damp under the rock before you water. Only water if it is dry under the rock.

The amount of drainage the soil provides is SUPER important. The soil should basically crumble and fall apart even when it’s wet so it doesn’t stay compacted and the water can flow through. I always add coconut chips (from my snake), activated charcoal chips, and (depending on what plant) perlite to help with drainage.

It also depends on where you live and what type of plants you have. I live in a somewhat dry area so my plants get thirsty fast. 50% of my plants are in containers with no drainage and they’re all thriving. I’m only considering repotting because they’ve outgrown their pots…

Soil can, has and does clog up drainage holes sometimes which causes water to sit in the bottom of the pot or drain out very slowly. Putting gravel in the bottom solves this problem.

I don’t think anyone believes putting gravel in the bottom of the pot makes the soil drain better because that is ridiculous. People put gravel in the bottom to ensure that any water that does drain all the way to the bottom can easily get out of the drainage holes which remain unclogged and virtually free of water absorbing soil. Gravel is no substitute for well draining soil. It is simply part of the equation that makes the draining system in the pot work more efficiently.

It is not a myth except for the people who believe that gravel at the bottom affects the drainage of the soil above it in any way. It only affects the water that drains through that soil and ensures it flows out the bottom unimpeded.

Hey Debbie, I’m not sure if you’re still looking for a way to disinfect the rocks or not but what I do is take a throwaway aluminium tray and stick the rocks in it to bake at 400° F for half an hour to an hour. But if you buy, say, decorative glass stones you shouldn’t have to do this.

After unsuccessfully looking for gravel in 4 shops, I found some on the side of the road, enough to put in the tray under my clay pots of rosemary. I just watered the rosemary and the water pooled up in the gravel. Should I soak it up, or is this ok? Did I overwater? I am determined to keep the rosemary alive this winter! And, is random gravel ok, or could it have chemicals in it that are bad for the plant?

I just got 2 Amaryllis’s, the pots they came in have no holes, should I replant it in a pot that has holes?

I have just gotten a large piece of property and I have a lot of questions. I understand that y’all can’t answer all but could you possibly tell me a site that can help me with lots of questions concerning a everything from deck container plants to in ground gardens, container gardens, etc…?

I’ve always had success with my flowers, vegetables etc.. In large pots I use a handful of charcoal my mother does this and so did my grandmother. The charcoal keeps certain kinds of plants from root rotting BC I have forgotten to do so and had this happen. I think it really depends on plants and climate I live in south close to beach where its very humid and alot of rain. The charcoal creates drainage and oxygen. I’m definitely no expert but have had success. I do have a question about Orchids? I got a beautiful phalaenopsis white orchid for Mothers day I’m never had one and I potted in miracle grow in a pot indoors it had done wonderful its thick and lush but it was in a small clear container with holes sitting inside another pot so I watered it let it sit for a while then drained it but the roots were busting out of pot so I just replanted it but then read it doesn’t like to be in bigger pot it likes to be crowded roots were starting to turn brown I clipped the dead off and put it in soil was this a mistake what should I put in it? I don’t want to loose it.

Brief explanation of PWT (perched water table), because PWT for pots is different from conventional reservoir PWT.
PWT – all pots have a PWT. It is the line where gravity is balanced out by saturation of the soil, and it is dependent on the type of soil. If you fill pots with heights of 6″, 12″, and 24″ with the same soil, the PWT will be at the same height (NOT percent of total height) in all pots. If the PWT is 4″, it’ll be 4″ in all pots. However, a good potting soil has many mediums present (e.g. peat) which aid the capillary action by wicking moisture from areas of high saturation to low saturation.

Now, about that “gravel is a myth” malarkey. The two primary reasons why using gravel (or stones of any kind, or a mesh, or whatever) is NOT a myth are these:

1) Air circulation. We all know that the more air permitted to circulate through the growing medium, the better it is for the plant. Let’s take a an average 8″ diameter pot with 8 holes on the bottom. That is not a great deal of surface area exposed to air if you fill the entire pot with soil, and the surface area is not well distributed. But, if you put a small layer of stones at the bottom, you are greatly increasing the surface area of soil that will be exposed to oxygen AND distributing that area in a meaningful way. This is the same reason every fish owner and hydroponic gardener (who uses methods more complex than Kratky’s) uses air stones. Something was said akin to “if you don’t believe me, take a sponge…” – well, try this: if you don’t believe ME, cut 2 sponges to fit in your pots, set one alone in a pot, and set one in a plastic container with stones at the bottom, and see which dries first.

2) Drainage. This is also about distribution of surface area. In a draining pot, there are flat areas between the holes. These flat areas are just like any flat area – nothing complex, it’s a piece of plastic, which for this example with be one square inch in size. This example is easy.
a) To simulate a draining pot with just holes: drip water onto your kitchen counter (can just run a hand under the faucet, but try to only move a few drops at a time to not disturb surface tension) and see how much it takes until the water is over a square inch in size? It’s a lot, isn’t it?
b) To simulate a pot with stones at the bottom: hold a fork flat to your kitchen counter and do the same thing. How much does it take before the water runs between the tines of the fork? Not much, is it?

————

Also, for drainage there is the issue of clogs from debris in the soil. In a regular draining pot with those 8 holes, one clog and you’re down almost 1/8 of your air circulation and water drainage. In a stone-lined pot, the impact is negligible as water and air will seep right around the debris because of the irregular edges of the stones.

Now, I completely understand why “gravel is a myth” seems logical at first glance. The author gave all the first glance reasons and they make sense. However, not all surface area is created equal. The other factors, molecular cohesion (why water naturally forms droplets instead of naturally misting), and surface area distribution are far more important.

The capillary action of moist soil is not enough to overcome the distribution stones offer. Hell, a FAN isn’t enough to overcome the kind of distribution factor at play here.

“Gravel is a myth” is a myth. You can go to the mattresses and defend it, but it’s just not true. It’s a crazy world and we’re always coming up with new ways to do things. Most of the time, it’s progress. But some of the time, there’s no school like the old school. So what if gardeners in the 1930s had never heard of “molecular cohesion”? They still knew that water drains better off the tines of a fork than it does off a flat surface.

The author of the article is right. Gravel isn’t necessary if your pot has drainage holes and it doesn’t create adequete drainage if there aren’t any. Well-drained potting soil is the key to most potted plants.

If I choose to put a few larger pieces of flagstone (maybe 2-3, 1-1 1/2 in pieces and then the good potting soil, the few rocks are just to put around the whole in the bottom to keep the dirt from running out of the whole. I have always done well with this. Is there something safe for plants that I could use to disinfect the rocks? Please help.

Rocks or pebbles are often used is the bottom of pots with with screen, mesh, old pantyhose cutouts coffee filters on top of them, for pots with no holes in the bottom. Because creative placement of potted plants would not work with pots with holes.

OK Everyone has made good and valid points. I think several methods with rocks have been passed down and not fully taught nor understood. Gravel or stone in average pot is for holes not layer. However you can enhance root growth by adding many different stones and or rocks specific to the plant and where it comes from. We are looking for trace minerals ok. Now I use lava rocks in the bottom of most fruit and flower I add lots of holes half way up the layer of rock ( So 2inch rock hole 1inch high on sides of container. IF POT HAS Holes on bottom block them water tight) Lava rocks retain water 1inch resavoir extra holes prevent over watering and adds air 1inch rocks(Makes 2inches) then promix. 1 week before fruit or flower add water and molasses feed directly to roots through holes MODESTLY Always half of manufactur suggested feeding measurements. (Gives plants a super boost to produce sugars and oils. SO MORE FLAVOR SMELL COLOR NATURALLY AWeSOME

I disagree with this article. I have talked to many nursery people and they have told me to use gravel and sand mixed with cow manure and compost. the proper way to actually do it is to mix everything not layer it. This year I used just potting soil and some of my plants never made it out of the bulb stage because they drown. So I mixed sand/cow manure compost mixture, gravel, cactus potting soil and regular soil. I am also going to add an powdered egg shell/coffee used coffee grind mixture and I have drilled several holes in my pots for both air flow and drainage

drainage problem developed and plant is dying is there anything i could do to save and rescue the plant ( a pot plenty of holes on bottem but god knows what is preventing drainage could be a paper plate and or all the above) help

Gravel at bottom does not improve drainage, and after watering (and a long while after that) bottom layer is saturated with water and oxygen moves 10000 times slower through water than air i e no oxygen that way.

Main item for getting much oxygen to roots is to have a large portion of pores with relatively large size (100-500um or so) which means the best thing toi do is to add e g gravel size 1-2 mm or at least 0,5-8mm (>8mm is ok but less good since roots will circulate it and thus lessen oxygen uptake). You must also avoid adding much fine grained substance since it will clog the big pores and then youre back at square 0

“perched weater table” is a funny name since there are no water tables in pots, just outdoors, but the ideas are correct also for pots and the saturated water layer att the bottom is there because of capillary action and surface tension

You have to go to a university library to get proper info, much confusion in internet forums and books on potted plants, and too complicated matter for forums like this. I am just writing a book on soil, sadly in Swedish though 😉

Can someone explain if my thinking is correct or why if it is not? I think gravel down the bottom helps drainage because it prevents the drain holes from getting blocked and preventing the soil from becoming water logged. It can allow for more air to reach the roots especially when used in conjunction with side holes at the bottom of the pots. Also i can’t understand any reasoning behind the “perched water table” theory, soil which has adequate drainage will only hold so much water thus will never be “too” wet for the roots and if it is “too” wet then i would think it would be the mixture of soil that was not correct for your particular plant and maybe has a too higher water retention in it rather than it being the gravel below it that could be causing the problem? Maybe even adding more gravel to the mixture of soil would help this further?
Any explanation or opinion would be very much appreciated.

You’re right about saturated water gathering at the bottom. However, when suggesting water under the pot increases humidity you are nurtering another myth. It does only do that in confined spaces, not in ventilated rooms like living areas, greenhouses or outdoors. Get a hygrometer and see for yourself. And the phrase “perched water table” I think is based on a misunderstanding by someone at the gradenweb forum. A water table is the level of water naturally occurring in the ground outdoors. The saturated water area at the bottom of pots doesn’t have a name that I know of, you can call it trapped water, saturated water area, or possibly perched water but without the “table”, although the word perched makes less sense in a pot than outdoors.

My problem is that when the outside pots are watered the soils drains too fast and flows out the bottom very quickly. I use high quality potting soil. The water has started staining the patio area. Just purchased saucers for the pots but they over flow if the plants are given a good watering. I live in Phoenix. Any suggestions to slow the water down from draining out so fast? The soil is not uniformly wet when the drip system is activated. Seems to go straight down and out.

We have 14 very large concret culverts 4 & 5. Ft. diameter , 2ft to 6ft tall. We filled them half full with native dirt then filled the top half with good planting soil. Irrigation is a bubbler at each. All but one is doing great, it’s the largest, at 5x6ft. The water just pools & won’t drain. It’s open at the bottom, sitting on native dirt. Only the one is having trouble. irrigation pipe is not broken. Any ideas to get it draining.

Serial plant killer here. On the typical self watering plastic container the holes in the base only line up correctly in one configuration. Why? Is it for the purpose of connecting only one or two of the holes to allow for airflow and better drainage? Thank you

We are beginning to plant vegetables in long colorbond planter boxes. There is no holes in the bottom so I need to drill some in the plastic base. The sides are corrugated colorbond. Instead of using filters as mentioned, what if I put a rubber mesh doormat in there, and then soil over that?? Will that act as an airator and drainage, and allow soul to natural breathe & drain thru the bottom??

Hi,
Can you help? I have a sandstone planter situated along the width of my swimming pool. The planter has been waterproofed and a series of drainage holes have been placed along the back wall of the planter (close to the bottom). Could you please tell me if this is OK and how should I proceed? What do I have to do to get the planter ready for planting?

the purpose of rocks in the bottom of the pot is not only to drain water off the bottom of the soil, but to help air get in to the roots. Plus if you have straight soil in the pot, then all the water setting in the bottom of the pot makes your plant un-happy. because it will have or get root rot from all the water, and you can drowned it out. I say put some rocks in the bottom, and mix some in your dirt so that it will resemble a more natural growing environment. plus mix in a little bit of sand to help keep the soil lose and workable for when you might have to aerate the roots. plus it will help keep the soil broke down for the plants to get the nutrients from the soil. if you use a good potting soil it probably will have sand in it. just read the label to see if it is in there. if not then just use a little bit of sand because it is already a good soil that is pretty well broke down. however, if you use just plain ol dirt then you may want a little more sand in it and work it over real good mixing it so the dirt won’t pack down and become hard. if the dirt gets to hard then water and air will have troubles penetrating to the plants roots.

I put Spanish Moss in the bottom of my pots to keep soil from spilling out the drain holes. Sometimes I use fabric pot scrubbers to cover the holes as well. I hope it works out okay since this is my first time doing it…if it doesn’t then I will have to try the coffee filters.

The gravel or sand is to keep the drainage holes from clogging, as Olafur and topkick noted. A coffee filter works as well.

If you want a water reservoir to protect the plant from drying out, put some sand in the bottom of a pot (with no bottom holes) and make drainage holes in the side of the pot near the top of the sand. When the soil is saturated, water will drain into the sand, fill the reservoir, and drain out the side when the reservoir is full. As the soil dries out, soil moisture will move upward from the sand into the soil by capillary action, at least until the moisture content reaches an equilibrium.

A perched water table forms when the fine-grained layer in beneath the coarser-grained layer, not the other way around.

What if you place a 2″layer of pebbles in the the bottom of the pot with a screen over that separating the the soil from the pebbles. Wouldn’t that create more surface area to drain (less likely for the drain hole to clog) and faster drainage than the single drain hole. I have done that for years and it seems to work fine.

OC Gardener is correct. Any time you have a fine material over a course material, with an abrubt change between the two, you will have a perched water table. If soil is “clucking up” the bottom of your pots the screen is key. This could cause a problem if your potting mix is not up to par. Fine clays can accumulate and settle in the bottom of the pot. So make sure your potting mix is properly proportioned. Some plants will thrive in a wet environment, but you will know that you have a perched water table when you try to grow a plant that requires very well drained soil.

It is a myth. Gravel at the bottom creates a perched water table. It does not improve drainage. If you want water to drain well, put a piece of screen over the hole. Don’t use gravel! If you don’t believe this article, look up perched water table. You will learn about this in any botany or horticulture class.

The gravel is used as a drain for pots so the water dont pool
up in the bottom of the pot, some times the dirt or moss do cluck up the drain holes on the pots. also do sterilize the gravel and dirt before using, there are inzect eggs and pezt you need to get rid off. better safe then sorry 😉

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Garden Myth: Gravel in Pots and Containers

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